Pigment



Patented May 7, 1935.

PATENT OFFICE PIGMENT Friedrich August Henglein, Cologne-Deutz, and

Oswin Nitzschke, Leverkusen-I. G. Werk; Germany, assignors to I. G.Farbenindustrie Aktiengesellschaft, Frankfort on the- Main,

Germany No Drawing. Application December 23, 1932, Serial No. 648,723.In Germany January 13,,

4 Claims.

The present invention relates to pigments being composed of chromiumoxide and alkalineearth metal sulfate in a fixed proportion, and to aprocess of preparing the same.

In accordance with the present invention it has been found that veryvaluable green pigments are obtained when reacting at elevatedtemperature upon an alkaline-earth metal chromate or bichromate with agas containing sulfur dioxide or sulfur trioxide; all alkaline-earthmetal monoor bi-chromates such as calcium, strontium and barium monoandbichromates come into consideration. The reaction proceeds according toone of the following equations: 7

(Me standing for Ca, Sr, Ba.)

According to this process products are obtained which display a muchpurer and greener shade than additional mixtures of chromoxide greenwith the corresponding alkaline-earth metal sulfates.

A further advantage of the process is the very simple working method.The alkaline-earth metal chromate is heated to a temperature of 700-1300C. for instance in a revolving furnace through which gases containingS02 or SO: are passed. The product on leaving the furnace does notrequire any after-treatment and can directly be used for painting. 7

The invention is further illustrated by the following example withoutbeing restricted thereto:-

Example Into a revolving furnace which is heated to 1150 C. bariummono-chromate is gradually .introduced so that it passes slowly throughthe furnace to the lower part of the same. At this lower end the-gasesobtained from roasting, that is to say gases containing S02 areintroduced into the tube in counter-current to the barium mono-chromatein order to leave the tube at the upper end. composed of 2 mols of B8504together with 1 mol of CI2O3, does not require any after-treatment forthe use as pigment.

The same product is obtained when taking, instead of gases obtained fromroasting, gases containing S03. When starting with barium bichromateinstead of with mono-chromate a prodnot of the following composition isobtained:

1 mol of BaSO4 to 1 mol of C1203,

which is equally well suitable as a pigment.

1. Process for preparing green pigments consisting in heating analkaline-earth metal chromate to a temperature of 700-1300 C. in anatmosphere containing SO 11 standing for 2 or 3.

.2. Process for preparing green pigments consisting in heating a bariumchromate to a tem- The mixture obtained, being perature of 700-1300" C.in an atmosphere con- FRIEDRICH AUGUST HENGLEIN. oswm NYITZSCHKE.

3. Process for preparing green pigments con-

